The present invention relates to polyhydric phenols and epoxy resins obtained using them as starting materials. The epoxy resins of the present invention are useful especially as encapsulants for electronic parts.
Recently, transfer molding of epoxy resin compositions which are economically advantageous has been carried out for encapsulation of semiconductors such as LSI, IC and transistors. Especially, surface mounting has been carried out for LSI and direct dipping in bath of solder has often been conducted. In this case, since encapsulants are exposed to high temperatures of higher than 200.degree. C., water absorbed and contained therein expands to cause cracking.
Therefore, epoxy resin encapsulants are required to be low in moisture absorption and have resistance to cracking and at present, glycidyl ethers of o-cresol novolak are mainly used. Further, encapsulants comprising glycidyl ethers of tetramethylbiphenol were developed to improve the moisture absorption. [Japanese Patent Kokai (Laid-Open) No. Hei 1-283241]
Moreover, glycidyl ethers of condensates of .alpha.-naphthol with aldehydes have been known as epoxy resins low in water absorption and excellent in heat resistance. Japanese Patent Kokai No. Sho 62-25116).
Encapsulants mainly composed of glycidyl ethers of o-cresol novolak are excellent in heat resistance and are somehow superior in balancing of heat resistance and low moisture absorption, but they are not necessarily satisfactory in the use which requires low moisture absorption of higher level as mentioned above and improvement has been demanded.
The glycidyl ethers of tetramethylbiphenol are superior in low moisture absorption, but are not necessarily enough in heat resistance. Therefore, they are limited in their use as encapsulants.
Furthermore, glycidyl ethers of condensates of .alpha.-naphthol with aldehydes are low in moisture absorption, but high in melt viscosity even in the case of low polymerization degree and inferior in operability and besides, insufficient in heat resistance.